It has to be a bug! *includes spoilers*

OK, Diablo really never showed up for me. I searched every corner of that sanctuary for other monsters I might need to kill first, and the place was empty. So I waited, for about 15 minutes. Then I went to act I, picked myself up a little boy's leg, returned to act IV to see if Diablo had felt like showing. Nope, no show.

Needless to say it was a very frustrating experience. Especially when you've been anticipating giving big D the smack down all evening. I'm not sure I have the patience to work my way inside the sanctuary again by myself tonight. What a bummer.

I think I might have TP'd out of the sanctuary at a bad time, because I did so soon after I killed the last minions (I wanted to rearrange stuff in my belt and prepare). When I came back, I hit the convenient experience shrine, hoping for a big bonus, and found myself totally alone.

Next time, no TPs, just kill everything and wait for his highness to show. If a higher level char wants to join and take care of some of those pesky minions for me, that might help the repetitive boredom of church sweeping...

Yeah. But one difference is that one of the sectors never generated monsters when I activated it (I activated the furthest one first - no monsters came).

Even wierder. I just hosted a tcp/ip game and had ogopogo help me go through and take out Diablo (this time we did closest to furhtest and monsters spawned in each area), but despite him dying I still have the quest and can't create nighmare level games on B.net. I think it may be because I didn't check the quest page and never had a chance to see the "quest completed" message. This is just a little annoying. Oh well, big D didn't drop anything interesting this time around anyway.

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You have to kill every unique monster before diablo appears. Sometimes the unique wraith will fly off into a corner above the lava.
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That's a possibility, but I'm pretty sure the group of knights and mages never spawned at all. In any case, if I had though more about it, I would have picked up a bow and spent another 15 minutes firing into the air around where the wraiths spawned just in case!